The present invention relates to a hard disk drive in which a magnetic head is brought into contact with a magnetic disk.
In hard disk drives (HDDs), data are magnetically recorded on a recording medium, i.e., a magnetic disk, which will be referred to as a disk, and are magnetically reproduced from the disk, by a magnetic head which will be referred to as a head. The head generates recording magnetic fields on the basis of information to be written when data are recorded, while the head detects recorded magnetic fields from the disk to be transduced into reproduced signals when data are reproduced.
In relation to the HDDs, various kinds of technics have been developed so as to increase their recording density. In particular, elemental technics relating to the head and the disk are indispensable to increase the recording density. More precisely, technics of minimizing the distance between the head and disk are receiving attention, in addition to technics relating to the head itself, such as a technic employing an MR (magnetoresistive) head as a reproducing head.
A conventional HDD generally adopts the CSS (contact start and stop) type in which a head floats above the data recording surface of a disk during recording and reproducing of data. In the CSS type, as shown in FIG. 18A, a head 20 is in contact with a disk 10 when the disk stops rotating On the other hand, when the disk starts rotating at a high speed, the magnetic head 20 floats by means of an aerodynamic force, so that recording or reproducing is performed by the head 20 floating above the data recording surface of the disk 10 as shown in FIG. 18B. At this time, the output signal level of the head 20 is increased with a decrease in a floating height FH, i.e., the distance between the head 20 and the disk 10.
In contrast to the CSS type, there has been developed a HDD in which a head and a disk are brought into contact with each other to minimize the distance between them. In this contact type, since the distance between the head and a magnetic recording region formed on the surface of the disk is zero, it is possible to relatively increase the output signal level. In other words, this contact type presents a small spacing loss, so that recording and reproducing can be performed at a considerably high density in principle. Generally, where the surface recording density of the disk is increased, the space distribution of a leaked magnetic field is decreased. As a result, the output signal level is decreased with an increase in the distance between the head and a disk.
In the contact type, however, since the head is in contact with the surface of the disk rotating at a high speed and slides thereon, the head is caused to stick to the disk where the flatness of the surface of the disk is high It is known that this sticking phenomenon is also caused even in the CSS type when its head and disk are in contact with each other. When the sticking phenomenon is caused, a problem arises in that the head cannot smoothly slide on the disk.
In order to solve such a problem, an up-and-down wavy pattern called "texture" is formed on the surface of a disk in the CSS type, so as to give a change to the surface shape or so as to increase the surface roughness. In this case, the wavy pattern of the surface texture is formed to have a short frequency relative to the track pitch, thereby suppressing fluctuation in the levels of the head output among track portions.
Therefore, even in the contact type, it may be effective to form such a surface texture on a disk for preventing the sticking phenomenon between its head and disk. Since the wavy pattern of a surface texture reduces the contact area between the head and disk, the sticking force is decreased.
However, in a case where the recording density is as high as a track pitch of less than 3 .mu.m, abrasion between the head and disk becomes prominent due to a surface texture having a short frequency described above. As a result, the head and disk are apt to suffer damages from fine powders generated by the abrasion.
Further, there is another problem in that a magnetic film and a protection film arranged on a disk are separated or damaged by a stress given by a head. It is thought that, in the contact type, this phenomenon is due to an extraordinarily long period of time in which the disk rotating at a high speed and the head are in contact with each other. Furthermore, medium noises due to a surface texture having a wavy patter of a short frequency are generated in the recording frequency domain of the disk, and thus can increase the error rate during data reproducing.